1. Field of the Invention
This invention relates to a method for removing the thermal-hardened frit seal to be used for assembling electronic parts. More specifically, the present invention relates to a method for removing the sealing material which is a kind of glass compound and is thermal-hardened by crystallization when soldering the parts.
2. Description of the Prior Art
This sealing material to be called as solder glass is also named as frit glass usually in the electronics industry.
The solder glass is widely used for sealing of panel and funnel which are parts of CRT(Cathode-Ray Tube), X-ray Tube, semiconductor chips, Integrated Circuits, etc.
When assembling the pads, glass compound can be used for sealing material. During sealing process, the glass compound to be placed between the parts is crystallized and hardened by heat, and then the parts can be completely sealed.
For example, in case of CRT, the composition of the glass compound(PbOxe2x80x94B2O3xe2x80x94ZnO) to be used for sealing the panel and funnel is PbO(75 to 82%), B2O3(6.5 to 12%), ZnO(7 to 14%), SiO2(1.5 to 3%), Al2O3(0 to 3%) and sometimes BaO, Na2O, LiO2(0.2 to 2%) can be additionally contained.
Also the other composition of the glass compound (ZnOxe2x80x94B2O3xe2x80x94SiO2) is ZnO(60 to 70%), B2O3(19 to 25%), SiO2(10 to 30 16%), and Al2O3 and MgO(2 to 2.5%) to be sometimes additionally contained.
The paste to be prepared by mixing the glass compound powder (PbOxe2x80x94B2O3xe2x80x94ZnO) with the special solution(for example, 1% isoamylacetate of nitrocelluous), is spread on the sealing place of funnel, and the panel is put onto the sealing place of funnel. When heating at the speed of 7 to 10xc2x0 C. per minutes up to 440xc2x0 C., the glass compound is melted and crystallized at 440xc2x0 C. for one hour. PbO as a component of glass compound is changed to be Pb3O4 at 370xc2x0 C.
The assembled panel and funnel(to be called as Bulb) is continuously processed to the next steps but there would be the defective bulbs during the process. These defective bulbs are collected and salvaged for re-use. For salvage, the panel and funnel should be separated and the crystallized sealing material (Frit) which is remaining in the panel/funnel should be removed. Conventionally diluted HNO3 solution(12 to 17%) is used for removing the frit and the method for removing the frit by using HNO3 is explained as follows.
FIG. 1 is the cross-sectional view of the frit in the panel and funnel (1a, 1b, 1c).
FIG. 2 is the enlarged cross-sectional view of frit (1a1b1c).
FIG. 3 is the process flow of separating of panel/funnel and removing of frit. FIG. 3(A) is showing the spray of HNO3 by nozzle (2a). The temperature of HNO3 solution is 35 to 70xc2x0 C. and the frit (1a) is removed by spraying for 2 to 4 minutes. FIG. 3(B) is showing that the frit (1a) is removed while the frit (1b) and (1c) still exist. FIG. 3(C) is showing the process of separation by using the hot water (nozzle 2b, 50 to 70xc2x0 C.) and cold water (nozzle 2c, 7 to 20xc2x0 C.). FIG. 3(D) is showing the removing of the remaining frit(1b, 1c) of panel and funnel which are dipped in the heated HNO3 solution and air bubbling method is used. FIG. 3(E) is showing another method for removing the remaining frit (1b, 1c) of panel and funnel by direct spray of HNO3 to the frit. FIG. 3(F) is showing the panel and funnel, the remaining frit of which are already removed.
An inspection is done after removing the frit, and if any remaining frit is found, such frit is removed again by mechanical polishing.
During the frit removing process as above, lead oxide and other oxides are reacting with HNO3 to be changed as lead nitrates and other nitrates which are dissolved in the solution.
The frit removing process needs spraying and bubbling of heated HNO3 solution, such condition of which causes the generating of the fume of nitric oxides (NOx:NO1 NO2). This fume is hazardous and corrosive that it should be properly collected and treated, for which the investment cost for protecting air pollution is needed.
A need to develop the substitute material of HNO3 in order not to generate NOx gas. Also total-nitrogen content of discharge water should be reduced according to the environment protection law.
The chemical reaction formulas between HNO3 and solder glass(Pb2O4, ZnO, Al2O3, BaO) are as follows.
6HNO3+Pb3O4xe2x86x923Pb(NO3)2+3H2O+1/2O2xe2x80x83xe2x80x83(1)
2HNO3+ZnOxe2x86x92Zn(NO3)2+H2Oxe2x80x83xe2x80x83(2)
3HNO3+Al2O3xe2x86x92Al2(NO3)3+3/2H2O+3/2O2xe2x80x83xe2x80x83(3)
2HNO3+BaOxe2x86x92Ba(NO3)2+H2Oxe2x80x83xe2x80x83(4)
Above formulas show the substitution reaction between H+ of HNO3 and metal ion. In addition to this chemical reaction, physical method such as stirring, air bubbling, spraying, ultrasonic, etc. to the HNO3 solution accelerates the generation of NOx. The reaction formulas are as follows.
2HNO3xe2x86x92H2O+NO2+NO2+O2xe2x80x83xe2x80x83(5)
NO+1/2O2xe2x86x92NO2xe2x80x83xe2x80x83(6)
By reacting as above shown formulas, the consumption of HNO3 is fast while generating metal nitrates in the solution and NOx gas in the air. Thus the concentration of solution is fast decreasing and life time of solution is shortened.
Hence it is another important subject to improve the solution life time and accordingly to reduce the volume of wastes.
Therefore it is an object of the present invention to provide a method to remove the frit without generating nitric oxides.
It is another object of the present invention to provide a method to extend the using life time of solution and to minimize the volume of wastes in the frit removing process.
In achieving the above objects, the method for removing the sealing material(solder glass or frit glass) in the manufacturing process of electronic parts, comprising the step of:
treating the sealing material with the acid or the salt which is containing sulfonic acid ion.